Many industrial processes produce olefin/saturated hydrocarbon streams that are mixtures of olefins, saturated hydrocarbons, and oxygenates. Olefins are frequently used in the manufacture of polymers such as polyethylene, as drilling mud additives, or as intermediates for the production of oil additives and detergents. Some industrial processes manufacture olefins streams by oligomerizing ethylene over an alpha olefin catalyst to produce mixtures of alpha and internal olefins having a broad range of carbon numbers. However, these streams rely on the use of ethylene as a feedstock material, which add a significant cost to the manufacture of the olefin. On the other hand, the FT process starts with an inexpensive feedstock, syngas, generally derived from natural gas, coal, coke, and other carbonaceous compounds to make oligomers comprised of olefins, aromatics, saturates, and oxygenates.
The FT process, however, is not very selective to the production of olefins. While reaction conditions and catalysts can be tuned to manufacture a stream rich in the desired species within the FT product stream, a large percentage of the FT stream contains other types of compounds which must be separated from the olefins, which olefins are purified, and then sold into different markets. For example, a typical commercial FT stream will contain a mixture of saturated hydrocarbons, olefins, aromatics, and oxygenates such as organic carboxylic acids, alcohols, ethers, esters, ketones, and aldehydes. All these compounds must be separated from the crude FT stream before a particular composition may be offered commercially. To further complicate the separation operation, the FT stream contains compounds having a wide spectrum of carbon numbers, as well as a wide variety of olefins, ranging from C.sub.2 -C.sub.200 species, internal linear olefins, alpha linear olefins, internal branched olefins, alpha branched olefins, and cyclic olefins, many of which have similar molecular weights. Separating and isolating these species is no easy task. Conventional distillation methods are frequently inadequate to separate species having closely related boiling points.
Various processes have been proposed to efficiently separate the different species in a FT stream with sufficient purity that a particular composition is acceptable in the intended application. These processes for separating out different species in a FT stream include the use of molecular sieves, which are restricted to a feed have an average carbon number range which is more limited than a composition containing a broad spectrum of average carbon numbers ranging from C.sub.5 -C.sub.20, to the use of exchange resins, to the use of super-fractionaters often operated at high pressure, and the use of oligomerization catalysts or etherification techniques to alter the boiling points of the species in the FT stream. Many reactive methods for separating species in a FT stream do not, however, selectively react with olefins while simultaneously reject paraffins.
U.S. Pat. No. 4,946,560 described a process for the separation of internal olefins from alpha olefins by contacting a feedstock with an adducting compound such as anthracene to form an olefin adduct, separating the adduct from the feedstock, dissociating the olefin adduct through heat to produce anthracene and an olefin composition enriched in alpha olefin, and separating out the anthracene from the alpha olefin. This reference does not suggest the desirability or the capability of anthracene to separate olefins from saturated hydrocarbons in a first step, or further separate the linear alpha olefins from the saturated hydrocarbons removed in the first step along with separating linear alpha olefins from an olefin stream removed in the first step.
As used throughout the specification and claims, the words, "first, second, third, etc" are meant only to distinguish one feed, composition, compound, or reaction zone, etc., from a different feed, composition, compound, reaction zone, etc., and are not meant to designate a particular sequence. For ease of tracking a particular stream and for convenience sake only, olefin streams have been assigned the letter "o," alpha olefin streams have been assigned the letters "ao," internal olefin streams have been assigned the letters "io," and saturated compound streams have been assigned the letter "s." Their presence does not imply a particular order, sequence, or ascribe a meaning to the description and claim language, nor does a letter's absence in a claim or embodiment imply that a process step or composition not expressly mentioned is required or implicit in the embodiment or claim. Where no spelled number or assigned letter is present, its use is not deemed necessary since other compounds, composition, steps, or reaction zones are not identically expressed in the embodiment or claim. Their absence or presence do not modify or ascribe a particular meaning, other than to differentiate from other identically expressed compounds, compositions, steps, reaction zones, etc in the embodiment or claim.